TF-38341: Add Admin Customization and General settings support

[sanjay-kansyakar-hashicorp]

Description

Adds ergonomic v2 client support for the admin Customization and General
settings singletons, exposing the new fields so Go automation (and the Terraform
provider) can read and update them programmatically.

New surface under Client.Admin:

• Client.Admin.Customization — Read / Update for /admin/customization-settings
  • New fields: InternalSupportURL, InternalDocumentationURL,
    InternalTutorialsURL, and AvatarSources
    ([]AdminAvatarSource{Source, Enabled}; currently only gravatar is valid).
  • SupportURL is exposed read-only (base fallback) and intentionally not
    updatable.
  • Update uses pointer options: a nil pointer leaves an attribute unchanged;
    an empty string clears an optional URL override so the default HashiCorp link
    is restored.
• Client.Admin.General — Read / Update for /admin/general-settings
  • New field: EnablePublicRegistration (TFE-only; silently ignored on HCP Terraform).

The Internal* URLs and AvatarSources are only meaningful on Terraform Enterprise;
on HCP Terraform they are zero-valued.

This change will be consumed by the Terraform provider in TF-38342
(tfe_admin_customization_settings / tfe_admin_general_settings resources).

The generated /admin/general-settings Kiota client lands via the nightly
API-update PR (#1494), which this PR is based on. Once #1494 merges to main,
this PR's base should be re-targeted to main.

https://hashicorp.atlassian.net/browse/TF-38341

Testing

Unit tests (httptest-based, no live TFE instance required) cover read, update,
and clear semantics for all new fields:

cd v2 && go test . -run 'TestAdmin(Customization|General)Settings' -v

Output

PCI review checklist

• I have documented a clear reason for, and description of, the change I am making.

• If applicable, I've documented a plan to revert these changes if they require more than reverting the pull request.
  Revert plan: this is additive (new Client.Admin.* surface + tests + CHANGELOG).
  Reverting the PR fully removes the feature with no data migration or state impact.

• If applicable, I've documented the impact of any changes to security controls.

  Examples of changes to security controls include using new access control methods, adding or removing logging pipelines, etc.

[hashicorp-cla-app]

All committers have signed the CLA.

[kosyfrances]

LGTM

[hamzahashicorp]

Left a comment on Admin setting grouping

The base branch was changed.

The base branch was changed.

[Uk1288]

It seems like there are now 2 entry points for this resource, the kiota generated and handwritten

client.API.Admin().CustomizationSettings()
client.API.Admin().GeneralSettings()

client.Admin.Settings.Customization
client.Admin.Settings.General

We should go with the generated ones to be inline with other existing resources. Or is there a reason why we need this resource to have 2 entry points?

[hamzahashicorp]

Hi Ukeme! thanks for the comment. After looking into it, I'm starting to wonder whether PR 1495 is even needed at all. From my understanding (and please correct me if I'm wrong), the Kiota generated client already covers the API endpoints this PR wishes to complete. For context: here is the JIRA ticket for it: https://hashicorp.atlassian.net/browse/TF-38341

The ticket targets v2, but uses v1 language. Since v2 work goes through the generated client, I think the ticket is effectively complete once the nightly regen lands the general-settings builder. Does that match your understanding?

[Uk1288]

that's right, once the nightly that contains your new API endpoints get merged, it becomes available via v2 so the ticket would be done.

[hamzahashicorp]

Closing this PR as the functions are already generated